Catalytic conversion process



W. D. SEYFRIED CATALYTIC CONVERSION PROCESS July 12, 1949.

Filed May 9, 1947 fj 1N VEN TOR A ORNEY.

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Patented July 12, 1949 UNITED STATES PATENT OFFICE CATALYTIC CONVERSION PROCESS poration of Delaware Application May 9, 1947, Serial No. 747,107

2 Claims.

The present invention is directed to a method for eliminating catalyst poisons from catalytic reactions. More specifically, the invention is directed to the catalytic dehydrogenation of hydrocarbons to less saturated hydrocarbons. In its more specific aspects, the invention is directed to the elimination of catalyst poisons introduced in the diluent employed in the catalytic dehydrogenation of hydrocarbons to less saturated hydrocarbons.

The production of butadiene from butylenes by dehydrogenation is a well known art. For example, it has been known to pass a mixture of normal butylenes over a suitable dehydrogenation catalyst such as nickel-chromium phosphate at temperatures in the range of 1100 to about 1300o F., said feed stock being diluted with steam to reduce the partial pressure of the butylenes and therefore minimize the formation of carbon on the catalyst. It has also been known to conduct the foregoing dehydrogenation reaction of hydrocarbons at space velocities of 150 volumes per volume of catalyst per hour to about 300 volumes of hydrocarbon per volume of catalyst per hour. Likewise, it is conventional practice to regenerate periodically the catalyst by burning of the catalyst by passing a mixture of air and steam over the catalyst in the range of 75 to 175 volumes of air per volume of catalyst per hour and at steam space velocities of 1500 to 6,000 volumes per volume of catalyst per hour. It is well known further to conduct the reaction in a plurality of catalyst cases with one catalyst case being on the reaction cycle and the other being on the regeneration cycle, thus allowing intermittent continuous operation of the dehydrogenation reaction; as soon as the catalyst in one reactor case loses its activity for the dehydrogenation reaction, it is taken off the reaction cycle and placed on the regeneration cycle and a regenerated catalyst case is placed on the reaction cycle, thus allowing the operation to be conducted continuously.

The reaction and the regeneration cycles are conducted at pressures from about to 10 pounds per square inch gauge although higher pressures may be employed if desired.

The amount of steam employed as diluent for the reaction is usually in the ratio of about to 20:1 or higher so that the reaction will occur with the proper partial pressure of hydrocarbons. If lower steam to hydrocarbon ratios are used, there is danger of substational carbon deposition on the catalyst with impairment of the efficiency and resultant shorter reaction cycles.

In conducting the foregoing type of reaction, it has been observed that poisons are introduced with the steam employed as a diluent. These poisons have been identified to be iron compounds which may be dissolved in the water used in generating steam or they may result from the steam eroding or corroding the lines through which it is conducted into the catalytic system. Regardless of the source of the poison, it is found that the presence of these small quantities of detrimental bodies or poisons, which have been identified in part as iron or iron compounds, substantially reduce the effectiveness of the catalytic conversion of butylenes to butadiene.

It is therefore the main object of the present invention to provide a method for removing poisons from diluents employed in the catalytic conversion of hydrocarbons.

Another object of the present invention is to provide a method for treating steam to remove iron and other detrimental bodies contained in it and make it suitable for use as a diluent in the dehydrogenation of hydrocarbons.

A more specific object of the invention is to provide a process for producing butadiene from butylenes by catalytic dehydrogenation of the latter in which longer periods of operation at lower temperatures and higher selectivities and at a higher conversion than possible heretofore by suitably treating the steam employed as a diluent for the reaction.

In accordance with the present invention, the foregoing objects are achieved by pretreating the steam employed in the catalytic conversion of hydrocarbons with an adsorbent material which selectively removes the poisons contained in the steam. Specifically, the present invention allows the removal of contaminating iron bodies from steam employed as a diluent in the catalytic dehydrogenation of butylenes to butadienes.

Briefly, the present invention may be described as involving the catalytic dehydrogenation of butylenes to butadienes in which a feed mixture of butylenes is heated to a temperature in the range of 1100 to 1300 F., following which it is admixed with a suitable amount of steam and passed into a dehydrogenation reactor containing a dehydrogenation catalyst. Prior to the admixture of the heated butylenes With the steam, the steam is heated to a temperature in the range between 1100 to 1300 F. and passed through a zone containing a suitable adsorbent, such as for example activated alumina, following which the treated steam is admixed with the butylenes and passed in admixture to the dehydrogenation zone.

The product issuing from the dehydrogenation Zone has its temperature reduced by passage through an oil quench tower and a water quench tower, following which the products are subjected to separation into a liquid phase and a vapor phase with the liquid phase being subjected toi an extractiontreatment with afsuitable. solvent for separation of the butylenes from butadiene and recovery of the latter. The vapor phase is also subjected to an absorption and a.

oxides ofcarbon and. lighter hydrocarbons. and:`

the. selectivity. of the reactionistherefore reduced sharply.

In. accordance. with'the present inventi-onait; has;

been found that contamination of' the catalyst.

with; iron or'other detrimental bodies or'poisons introduced with the'` steam diluent may' beeliminated; by pretreating` the; stearm ahead ofthe reactionzone With activated alumina or other suitable adsorbents which may be a' small portion: of

the catalyst itself; used in-b the dehydrogenation.

zone. While activated alumina. has been'v conveniently used; other adsorbentsr suchasv natural;

clays illustrated: by kieselguhr, kaolinite., diatomaceous earth, gibbsite,l montmorillonite;y and various other similar adsorbents may bef used. The material .employed,topretreatthe steam-.may bea smallportion of thescatalyst itself or iti-may be a small portionof spentI catalyst; provided thespent catalyst has not lost. its ability to. adsorb further quantities of' the. contaminating-Y. bodies ordinarily present inthe steamdiluent.

An embodiment of the present inventionl Will now be-described in conjunction With/-the-dra-wing inwhich the soleY figure is inithe form of. a. diagrammatic flow sheet' Turn-ing now. specifically to thev dra-Wing, a hydrocarbon feed stream which may, `for. purposes of example, be a-mixture of normal butylenes is introduced: intov the system through. line I2 controlled. by valve I3. The feed-hydrocarbon passes from linel I2` into line I1. andthence` into furnace I8- where it. is heatedtoa tempera.- ture inv the range-between 1150 and1f300.-F. The heated hydrocarbons issue from. furnace I3; by way off line I9' and are admixed. therein with steam introduced byline I; andft'he mixture then.

oWs to dehydrogena-tion Zone-2I-wheretis-subjected-to dehydrogenationfconditions to cause the formation of less saturated materialfrom the-feed hydrocarbon. In this particular instance,v the less saturated.- materials formed from the feedhydrocarbon will be. butadiene. I

The steam introduced'. into the systemA by way of line I5 intofline I9; which passes intofthe dehydrogenation zone 2I, is introducedy into.V the system by way of line 48. It passes by Way of line 48 into a furnace 41 whereits temperature is raised to a temperaturein the range ot 1-150? toA 1300 F. Thekheated'steam emergesfrom furnace lll by Way of.v line --and'thenpasses-into1 aA pretreating Zone I.4. whichL ma-yicont/aina suitable adsorbent of the type illustrated above. Briefly, zone I4 contains an adsorbent such as activated alumina in suflicient quantities to remove poisons which may be contained in the steam. These poisons are usually iron or its compounds, but other contaminating bodies may be present therein. Asipointedrout before,.regardless of the identity of the poisons, adsorption or pretreating Zone I 4 effectively removes them from the steam on passage therethrough. The effluent from pretreating. zone.. I4., is discharged by way of line I5 into line I9 where it is admixed with the heated hydrocarbonsy and serves as a diluent for the dehydrogenation. reaction.

Following the dehydrogenation step, the temperature of the reaction products and the steam from. the reaction zone is reduced as rapidly as possible by the introduction of a water spray into the. lowerI portion of the dehydrogenation reaction zone by means of line 22, a heat exchanger 23; an oil quenching zone 24f-and a4 water quenching-Zone 25. Themixture ofy hydrocarbon reaction products7 and steam'isy withdrawn from dehydrogenation reaction. zone 2| by line. 25 and passed tothe heat exchanger 23,` which isin the form ofa wasteheat boiler and is passed thence vialine21.tofoilfquenching zone 24. The vapors from *the oil quenching; zone pass through line` 21a and .intoseparator 28 toseparate water fromv the hydrocarbons and the vapors are passed' on through line 28 to-water quenching tower 25. Vaporsfrom. water quenching tower 25 are withdrawnthroughline.3|), passinto a second settling drum..3I.1to-remove condensate from the vapors, andthence throughrline. 32. containing compressor 33 and.v cool'er'34into. separating Vessel 35.

Theliquidaccumulating inivessel 35is. the desired- C4. fraction and-is withdrawnfrom the bottom of thiss vessel through. lne-3.. containing pump 3l andheater. 3B. andi'nto. distillation tower 39, where the butadiene. fractionmayy beremoved. as a side stream through line 401. A heavier fraction is withdrawn fromthe bottomof. the tower through line. 41I and a` lighter fraction. through line 42.

The. desirable traction from side stream may.

be sent, tov abutadi'ene extraction tower 43;. a finished" butadiene stream iswithdrawn from the extraction tower through outlet 44. and a fraction comprisingessentially butylenes is withdrawn from the extractionp-lant'via line I6l for admixingwith other. fractions to form the feed as has been before described;

It. is desirable to obtain Vat least a portion. of thesteamsent to the dehydrogenation zone from thewaste heat'bo'iler 231 andthis may be done by passing water" into theV boiler through inlet 45 and'. steam is. withdrawn from the boiler 23 through line 46th furnace 41 where it isheated to a suitable.,temperatureand then admixed by means of. line 2'02with the hydrocarbon feed flowinginline I9; Ifjsucientsteamfor the process is not produced by boiler 23 additional steam may be ad'dedto the system by inlet .4'8`.

It` is preferred to. voperate oil' quenching. tower 21km conjunctionwith. an absorber. unit de. In

theV separating vessel.35 for. separating the C4y fraction as a liquid', the. uncondensed fraction may contain appreciableamounts oflC'rhydrocarbons.. Itis., desirable to remove these. hydrocarbon. vaporsA throughline 1 5I. to. absorber vessel 5.3, where. they flow, countercurrent .to a. stream of oil. injected throughthe top ofk the.. absorber` by line. 52. The unabsorbed vapors. from. vessel 53. may be removedfrom thefsystem via. outlet. 53.

Ther-.ich .absorber oil...fromivesse1. 5.0 mayV be. with drawn through line 54 and returned to the top of quench tower 24 to serve as a quenching oil therein. The oil falling to the bottom of tower 24 is removed through line 55 containing pump 565 and the stream split, with a portion being added to the oil flowing in line 54 by means of connection 51 and the mixture used as the quenching oil and the remainder flowing through branch line 58 to stripping tower 59. In the stripping tower, the lighter constituents are removed from the oil and returned to the quenching tower through line 85 and the lean oil is removed via line 52 containing pump 6I and passed into absorber tower 50. If desired, a make-up lean oil may be added to the oil being circulated in line 5f! by inlet 62. The water quenching tower 25 is conventional, and is provided with water circulating line 63 containing pump 64.

The following is given as a specific example illustrating the practice of the present invention. A mixture of butylenes was heated to a tempera.- ture in the range between 1100L7 to 1250 F. prior to passage over a dehydrogenation catalyst which included nickel-chromium phosphate. Steam heated to a similar temperature was employed as a diluent for the reaction. The operation was conducted in cycles with one hour on reaction and one hour on regeneration. Thus a cycle length totalled two hours. Regeneration was accomplished by passing a mixture of air and steam over the catalyst diuing the period of one hour on the regeneration portion of the cycle. The pressures employed were in the range from 0 to 10 pounds per square inch. The foregoing operation was conducted with the steam being pretreated in the zone equivalent to pretreating zone I4. A comparison run was conducted with the pretreating zone eliminated. The data in the following table shows respectively the conventional operation without the pretreating zone I4 and the practice of the present invention employing pretreating Zone 54 with activated alumina as the absorbent.

1 Reaction and regeneration. 2 Uncorrected for polymer, acetylenes, and regeneration CO2.

It will be apparent from the foregoing data that" when the steam diluent is pretreated in accordance with the present invention, the temperature required for a 30% conversion for a comparable operating period is reduced by 14 F. and the selectivity at 30% conversion is increased by 9%. It is also apparent from the data that, with a lower catalyst temperature as allowed by the present invention, the operation may be conducted for a longer period than in conventional operations since the temperature may be gradually raised as the catalyst efciency is lowered. Since the present invention allows lower average catalyst temperatures, it is apparent that the temperature may be raised over a longer operating time than was possible heretofore to the maximum temperature allowable in the dehydrogenation reaction.

The selectivity increase also shows that greater amounts of the desirable product may be obtained in the practice of the present invention than was obtainable heretofore.

Although the example illustrates the effectiveness of activated alumina as a pretreating medium in a reaction involving contact with nickelclnomium phosphate catalyst, it will be apparent that a nickel-chromium phosphate catalyst itself may be used as a pretreating medium since observations have been made that the nickel-chromium phosphate catalyst is a good absorbent for iron and its compounds.

As another example oi the application of thel present invention in the dehydrogenation of butadiene from normal butylenes is the employment oi a catalyst comprising magnesium oxide, iron oxide, and potassium and copper oxides. This catalyst is employed in proportions of 80% magnesium oxide, 14% iron oxide, 3% potassium 0X- ide, and 3% copper oxide. In the particular instance when this type of catalyst is employed, it may be employed in pretreating Zone I4 or the dehydrogenation Zone 2l. As another example, a catalyst comprising 96% iron oxide, 5% potassium oxide and 5% of copper oxide may be employed in the pretreating zone I4 and the dehydrogenation zone 2i. n the last two examples, the two catalysts mentioned may be employed in dehydrogenation zone 2I and activated alumina or other absorbente of the type mentioned above may be used in the p retreating zone I4. The process steps when employing the catalyst used in the preceding examples are similar to those employed when using the nickel-chromium phosphate catalyst except that air is omitted during the regeneration step. When employing the predominantly iron oxide catalyst, higher steam to hydrocarbon ratios are necessary and the reaction is continuous, the regeneration cycle being omitted since the latter catalyst does not require regeneration.

When using either the predominantly magnesium oxide or iron oxide catalyst in the foregoing examples, it will be apparent that iron, since it is a component of the catalyst, will not be the poison to the reaction. In this particular instance the poisons introduced into the reaction sone 2| are chlorides which may be present either in the hydrocarbon or the steam. It is well known that commercial steam ordinarily includes chlorides in View of the presence of salts of various metals in water used for generating steam. In the practice of the present invention, it is possible to provide a substantially chloride-free steam for employment as a diluent for the reaction.

Similarly, chlorides may be present in the hydrocarbon feed and in these particular instances it may be desirable to pass the steam-hydrocarbon feed mixture rather than the steam alone through the pretreating zone I4. This may be accomplished by locating the pretreating zone I4 in line I9 rather than as shown in the drawing. The presence of chlorides in the hydrocarbon feed may also be encountered when the hydrocarbon feed is obtained from a catalytic process using halogens such as methyl chloride, aluminum chloride, or hydrogen chloride as diluents, catalyst, or promoters for various catalytic reactions.

It will be further understood that the preceding examples are given only by way of illustration and not by way of limitation. Instead of the dehydrogenation catalysts used in the example,

annees@ amt suitable catalyst may be. employed. Whichz. is known. tu. the dehydrogenation art. Similarly,L the temperatures of; the.' dehydrogenation reacition are not to be. restricted'. tn-L those given inrtlie examples.' but' may. be: variedc' from approximately 10.05?" tm. 13.0.0?" F." if desired.`

The; present invention. has; been described. and.

illustrated.: by' reference.' to dehydrogenation of hutyienes'- to butadiene and is given for' purposes. of; illustration and is not'. intended' as' a'- limita tion of'-V the; broad invention disclosed; herein. The pretreating operation. in which the diluent for a catalytic conversion operation is freed` of poisons for. the reaction is' believed to= bev applicable tuawide variety of processesemploying diluents. examples' ofv other catalystic processes:

toiwhi'ch: the' present invention may be applicable may be'- mentionedcatalytic' conversion in the presence of` hydrogen as diluent such as illus--v tratedf' by. the hydroformingV and hydrogenation 211 processes.

Wliilesteam has been described-andi illustrated asv a diluentfbr' the reaction, it is Within the scope of' the present' invention to'employ other diluents for thereaction. For example; itmay bef desirable co-employ nitrogenfand other rel-atively inert gases in lieu of steam.v The inert gases'y should" be substantially unaffected by-f the de'hydro'genation catalyst and should' serve to reduce' the partial pressure of' the hydrocarbons inithe' reaction zone.

usediorthereaction may be mentioned hydro'- As examples of the' typesH off diluents other than steam which maybe 8T. caribous such as: methane, ethane.,pinna-ne;and;V nitrogen-carbon dioxide and the;v like.

The nature. and objects,` of the: present inventian; having; been'. fully describedand` illustrated',

1 What'..-I,.Wish toclai-m as new. and'. useful and to.

secure by Letter-'sa Patent is:

1'; A. method. for producing butadiene' which..

REFERENCES. (LI'IEI)E 25: The following references' are of' record inthe file' of' this" patent:

UNITED STATES PAYIENTS' Number Name Date 3m 232422627 Strickland l\7[ty`2()"1941- 2i2`65,641' Grosskin'sky etal.' Dec: 9,' .194'1' '25269,0'28' Liedholm' et' al'. Jan. 6`, 1942" 233222857' 

